The invention relates to the field of coating products with particulate material. The application of such a coating takes place, inter alia, in the food industry. The application of a coating of flour to a meat product, such as hamburgers, schnitzels and the like, can be mentioned by way of example. Another example relates to the application of a coating of breadcrumb material to such products.
In all these applications the products to be coated are usually transported through a machine, for example a flour-coating machine or a breadcrumb-coating machine, by means of an open conveyor belt. With this arrangement the products located on the conveyor belt are fed through beneath a feed for the particulate material in such a way that they are covered with said material. The particulate material is applied with a certain surplus. This is important with a view to obtaining complete coating of the products.
The particulate material that lands on the conveyor belt between the products falls through the openings in the conveyor belt and is collected in order to be recirculated. However, the material that is on the products would remain on top of these and be transported out of the machine with the products. This is not desirable since a large proportion of the particulate material, that constitutes the surplus, would then be lost and could not be recirculated.
For these reasons the surplus particulate material is blown off the products in the machine in such a way that this surplus material is also able to fall through the openings in the conveyor belt and can be collected for recirculation. In this way as little as possible material is lost.
Various effects arise as a consequence of blowing air into the machine. First of all, blowing leads to dust formation. As much as possible of the dust formed has to be collected in the closed housing of the machine. Furthermore, an overpressure can be produced in the housing as a result of blowing. However, overpressure must be avoided since the dust particles would issue from the housing in the event of overpressure. For this reason there is a suction connection on the housing, by means of which a slight vacuum can be maintained. The air drawn off is filtered before it is discharged into the environment.
The known installation described above has various disadvantages. First of all a fairly large amount of power is needed to maintain the blowing stream and the suction stream. Furthermore, the filter has to be cleaned or replaced fairly frequently, since the quantities of air containing dust that are drawn off are fairly large.
The aim of the invention is to overcome these disadvantages. Said aim is achieved by means of an air unit for the removal of surplus particulate coating material that is present on products that are in a coating machine, which air unit comprises at least a blowing member for blowing surplus particulate material off the products, at least one suction member for drawing off air, with particulate material contained therein, from the coating machine, separating means for removing particulate material from the air drawn off, and circulating means for feeding at least a portion of the air drawn off to the blowing member.
The air unit according to the invention serves for blowing surplus particulate material off the products, for suction in order to reduce dust formation and also for maintaining a vacuum in the closed housing of the machine. With this unit the major proportion of the air drawn off is circulated. The quantity of air to be discharged into the environment consequently remains restricted, so that the filters can be of limited size and have to be cleaned or replaced less frequently.
The circulating means comprise a pump, the suction side of which is connected to the suction member and the blowing side of which is connected to the blowing member. Preferably the pump is a centrifugal pump which has a volute casing as well as an impeller that can be rotated with respect to the volute casing and is connected to an electric motor.
In connection with cleaning of the air unit it is highly desirable to make the various components thereof, such as the pump, readily accessible. Therefore, the volute casing is preferably mounted by means of a first frame on a chassis, which first frame can be hinged between an operating position and a folded-back position. In addition, the impeller and the electric motor connected thereto can be mounted on the chassis by means of a second frame, which second frame can be hinged between an operating position and a folded-back position.
The first frame and the second frame are hingeably mounted by means of hinges which are positioned on the chassis with respect to one another in such a way that the frames are located one on top of the other in the operating position, and the impeller is located in the volute casing. In the operating position the first frame is underneath the second frame.
The pump can be cleaned easily by first folding back the second frame with the motor and the impeller. In said folded-back position both the impeller and the volute casing are readily accessible for cleaning and inspection. The residues present therein can easily be sucked out using, for example, a vacuum cleaner hose. Cleaning by means of fluid and the like is also possible.
By folding back the first frame, the components located below the pump are then also readily accessible. The components concerned here are in particular the separating means. These means preferably comprise a cyclone provided with a casing that is symmetrical with respect to revolution and has a tangentially located feed, a core which extends centrally in the casing at the level of the feed, and collection means, for the particulate material, located at the bottom of the casing.
In this embodiment the first frame with the volute casing of the centrifugal pump is located on the top of the cyclone casing; the core is also fixed to this first frame. By folding back the frames the cyclone can now also be made readily accessible for cleaning and the like.
The collection means for the particles separated off can be connected to the bottom of the cyclone casing. These collection means comprise a container that is connected to the casing via a flap or slider. By closing the flap the container is temporarily closed off from the casing. As a result it is also possible to remove and empty the container while the air unit is in operation.
The blower unit can contain a dust filter. The surplus air can be blown through this filter, which removes virtually all particles, into the environment.
The invention also relates to the combination of the air unit described above and a coating machine intended for applying particulate material to products, comprising a housing, a conveyor belt, that extends through the housing and is provided with openings and on which the products can be transported through the housing, in which housing feed means are located for feeding particulate material onto the products located on the conveyor belt, at least one blowing member for the air unit, which blowing member is located above the conveyor belt for blowing air into the housing and over the conveyor belt, and a suction member for the air unit for drawing air out of the housing.
Partitioning means are provided in the housing, such that each blowing member is on one side of the partitioning means and the feed means are on the other side of the partitioning means.
In order to counteract the escape of dust from the coating machine, the combination described above is operated in accordance with the steps of delivering a quantity of air per unit time to the housing that is less than the quantity of air removed from the housing in such a way that a vacuum is generated in the housing.